Rangers assistant general manager Thad Levine said tests revealed no structural damage and that the issue was muscular. Lee received a trigger point injection, which the club hopes will reduce inflammation and allow him to stay on track.
The Rangers want to see how Lee reacts to his bullpen session Saturday. His next scheduled start was moved from Monday to Tuesday, giving him an extra two days of rest. Tommy Hunter will now start Monday in Toronto.
"He's going to join us on Friday and we'll see where he is," Levine said. "At this point, he's still on track to make his start next week."
Levine said Lee mentioned his back had been bothering him even before Tuesday's game. That might explain why he's struggled with his performance in his last five outings. Lee is 0-3 with an 8.28 ERA in that span and threw just 4 2/3 innings on Tuesday, his shortest outing since September 2009.
Lee is 2-5 with 72 strikeouts and a 4.69 ERA in 11 starts for Texas, which acquired him from the Seattle Mariners in July. For the season, he is 10-8 with 161 strikeouts and a 3.37 ERA.